1. Field of the Invention
The present invention relates to a pressure sensor for detecting liquid pressure and also relates to a pressure-differential flow rate meter and a flow rate controller provided with this pressure sensor.
2. Description of Related Art
In the related art, there are known pressure-differential flow rate meters in which an orifice plate is installed somewhere in a piping flow path, and the flow rate of liquid is measured by measuring a pressure difference between an upstream side and a downstream side of the orifice plate. In addition, there is a known flow rate controller that adjusts the degree of opening of an electrically actuated valve or the like on the basis of the flow rate detected by a pressure-differential flow rate meter to thereby perform control so as to maintain a predetermined flow rate (for example, see Japanese Unexamined Patent Application, Publication No. Hei 5-233068).
In the above-described pressure-differential flow rate meter, for example, as shown in FIG. 8, a pressure sensor 1 that detects liquid pressure is configured with a pressure measuring unit 4 disposed at a distal end of a pressure inlet pipe 3 which is branched in a T-shape from a main fluid flow path 2.
In addition, in some cases, the above-described pressure sensor 1 handles, for example, a high-temperature fluid of 80° C. or higher or a fluid that pulsates in a flow path; furthermore, the sensor may be affected by fluid hammer, depending on the configuration of the main fluid flow path 2. Therefore, in order to maintain preferable measurement conditions for the pressure sensor 1, it is necessary to devise damage reduction measures, such as measures against high-temperature fluids, fluid pulsation, or fluid hammer, in accordance with the installation conditions of the pressure sensor 1 and the state of the fluids (fluid type, temperature condition, or the like).
In conventional pressure sensors, as in a pressure sensor 1′ shown in FIG. 9, specific damage reduction measures include, for example, reducing the pipe diameter of a pressure inlet pipe 3A, making the pressure inlet pipe 3A longer to separate the pressure measuring unit 4 from the main fluid flow path 2, or a combination thereof.
In some cases, the above-described pressure sensor is used in a piping flow path in which a high-purity reagent and purified water alternately flow, for example, as in a semiconductor manufacturing apparatus. In the case of such a semiconductor manufacturing apparatus, cleanness of the liquid used and uniformity of wafer processing are critical; therefore, liquid displaceability in the piping flow path is extremely important. That is, when the fluid to be flowed in the piping flow path is changed, any residue of the previously used fluid will cause a loss of cleanness; therefore, it is necessary to perform complete displacement by washing until there is no residual liquid remaining.
However, when performing displacement by washing, the damage reduction measures described above form a relatively large dead volume where the previously used liquid tends to be retained. In particular, the pressure inlet pipe, which is long and narrow, is a space that becomes a dead volume where displacement is difficult during washing; therefore, in order to enable application to, for example, a semiconductor manufacturing apparatuses, the above-described damage reduction measures need to be improved.